Signal generator with frequency offset unit in the base band

ABSTRACT

A signal generator comprises at least one first base band unit and a second base band unit, generating a digital base band signal. At least one first frequency offset unit, connected to the first base band unit, which adds the output signal form the second base band unit and the output signal from the frequency offset unit and an I/Q modulator, in series with the addition unit are provided.

FIELD OF THE INVENTION

The invention relates to a signal generator, in which a digital baseband signal is first generated by means of a base band unit, andsubsequently—optionally after the insertion of units capable ofsimulating a transmission channel e.g. with fading, distortion andnoise—supplied to a I/Q modulator.

BACKGROUND OF THE INVENTION

In mobile telephone technology, a broad-band amplifier, which can beused to amplify several mobile telephone signals at the same time, isincreasingly used in order to economise on costs. For instance, two ormore W-CDMA (Wideband—Code Division Multiple Access) signals positionedon different frequency bands, or a GSM signal and a W-CDMA signal may berequired at the same time. In order to test a power amplifier in a basestation, for example, this power amplifier must be supplied with ameasurement signal, which simulates the operational situation as closeto reality as possible, i.e. with a combined signal derived from the twoabove-named individual signals. For this purpose, the individual signalshave, hitherto, been generated in separate signal generators as separatehigh-frequency signals, which are then combined at the output of thesignal generators, i.e. at the high-frequency side. This raises theproblem of synchronising the two separate signal generators. Moreover,it is disadvantageous that several signal generators are needed, becauseit is difficult to operate several separate devices, and the devicesrequire complex wiring at the output side.

Regarding background art, reference is made, by way of example, to U.S.Pat. No. 5,465,050, wherein the output signal from a signal generator iscombined on the high-frequency side, via a resistor network, with theoutput signal from a noise generator.

SUMMARY OF THE INVENTION

The invention addresses therefore a need for creating a signalgenerator, capable of generating digitally-modulated signals modulateduniformly or differently and positioned in different frequency bands ina simple manner.

According to an embodiment of the invention, at least two base bandunits are provided, wherein the output signals from the base band unitsare already offset relative to one another in the base band, and whereinthe base band signals offset with regard to their frequency position areadded. For example, two W-CDMA signals can be generated, which areoffset in their frequency position by a few MHz relative to one another.

The advantage of this procedure is that the combined signal can begenerated with a single signal generator, and several signal generatorsneed not be interconnected at the high frequency side. This ensures easeof handling.

The base band units can be controlled in a synchronous manner by acommon control unit, i.e. by a common microprocessor, a common digitalsignal processor or a common synthesiser. There is therefore nosynchronisation problem as encountered when using two separate signalgenerators. Optionally, approximately the same setting may be adoptedfor both base band units, and the user need only adjust the appropriateparameter once on the device for both base band units.

A base band generator, to which external signals can be supplied(analogue or digital, e.g. I/Q-data or an intermediate frequency signal)can be provided. The digital base band signal, which is generated fromthis externally supplied signal, can also be offset in frequency.

Furthermore, units which simulate certain channel properties, e.g.fading units, noise units or distortion units can be inserted betweenthe base band units and the I/Q-modulators. In this context, as analternative, the base band signals need not be added to the combinedsignal until after the fading units and/or the noise units.

Still other aspects, features, and advantages of the present inventionare readily apparent from the following detailed description, simply byillustrating a number of particular embodiments and implementations,including the best mode contemplated for carrying out the presentinvention. The present invention is also capable of other and differentembodiments, and its several details can be modified in various obviousrespects, all without departing from the spirit and scope of the presentinvention. Accordingly, the drawing and description are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is described in greater detailbelow with reference to the drawing. The drawing is as follows:

FIG. 1 shows a block circuit diagrams of an exemplary embodiment of asignal generator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The signal generator 1 provides a first base band unit 2 a and a secondbase and unit 2 b. The base band units 2 a and 2 b generate at their Iand Q outputs base band signals according to predetermined standards,which can be selected by the user, for example, according to the GSMstandard, the GSM-EDGE standard or the Wideband-CDMA standard. The baseband signals 2 a, 2 b can be supplied with clock signals at bushes 3 aand/or 3 b; trigger signals at bushes 4 a and/or 4 b; and modulationdata at bushes 5 a and/or 5 b. Alongside these, in the exemplaryembodiment illustrated, a digital base band generator 6 is provided,which generates the I- and Q-components of a further base band signalfrom digital I/Q-values supplied to a bush 7. The output signal from thedigital base band generator 6 can be frequency-offset via amultiplication unit 8 c, to which the adjustable frequency of anadjustable local oscillator 9 c is supplied. The multiplication unit 8 cand the local oscillator 9 c therefore form a frequency-offset unit 40c.

The optionally frequency-offset base band signal from the digital baseband generator unit 6 is supplied via a first switch element 10 a and/ora second switch element 10 b to a digital addition unit 11 a or adigital addition unit 11 b.

The output signal from the base band unit 2 a is supplied to amultiplication unit 8 a consisting in each case of a multiplier for theI-component and for the Q-component. The adjustable frequency of anadjustable local oscillator 9 a is supplied to the multiplication unit 8a. Accordingly, the digital output signal from the base band unit 2 acan be frequency-offset if required. If no frequency offset is required,the multiplier of the multiplication unit 8 a can be bypassed by meansof switchable rerouting lines. The output signal from the multiplicationunit 8 a is supplied to the addition unit 11 a.

In a similar manner, the output signal from the base band unit 8 b issupplied to a multiplication unit 8 b, consisting in each case of amultiplier for the I-component and the Q-component. The multipliers ofthe multiplication unit 8 b are connected to the adjustable localoscillator 9 b, so that the frequency of the digital output signal fromthe base band unit 2 b can be frequency offset if required. If nofrequency offset is required, the multipliers of this multiplicationunit 8 b can also be bypassed by means of switchable rerouting lines.The output signal from the multiplication unit 8 b is supplied to theaddition unit 11 b.

The output from the multiplication unit 40 a can also be connected via aswitch element 41 a to the addition unit 11 b, while the output from themultiplication unit 8 b can be connected via a switch element 41 b tothe addition unit 11 a.

In this manner, the output signals from the base band unit 2 a, the baseband unit 2 b and the base band generator 6 can be frequency offsetindependently from one another and added with a frequency-offset eitherto the addition unit 11 a or the addition unit 11 b.

The output signal from the addition units 11 a and 11 b can be suppliedvia a switch element 12 a and/or a switch element 12 b to a fading unit13 a and/or 13 b, which applies fading (variable decrease) and/ordistortion to the base band signal. The functions of the fading units 13a and 13 b, such as the number, the time delay and the damping of thesignal-delay pathways implemented in the fading unit, can be determinedby the user. The fading units 13 a and 13 b are each connected via anaddition unit 14 a and/or 14 b to a noise unit 15 a and/or 15 b. Thenoise units 15 a, 15 b apply a noise signal, which can be determined bythe user, to the base band signal. For example, the type of noise andthe level of the noise signal generated by the noise unit 15 a, 15 b canbe selected by the user.

The output signals from the fading units 13 a, 13 b can also be addedand in each case supplied to one of the two noise units 15 a and/or 15 bvia a switch element 16 connecting the addition units 14 a and 14 binstead of connecting the relevant fading unit 13 a and/or 13 bseparately to the allocated noise unit 15 a and/or 15 b. The I/Q outputsignals at the output of the noise units 15 a and/or 15 b can beextracted at bushes 17 a and 18 a and/or 17 b and 18 b.

The output signals from the noise units 17 a and 17 b can be supplied toI/Q-modulators 20 a and/or 20 b via addition and switch units 19 a and19 b. In this case also, the output signals from the noise units 15 aand 15 b can be added via a switch element 21 and supplied to one of thetwo I/Q-modulators 20 a and/or 20 b. Several user-specific selectionoptions are also available with regard to the function of the I/Qmodulator 20 a, 20 b. For example, the I/Q-modulator 20 a, 20 b can beoperated to generate a burst sequence, and the active bursts and/or thelevel of the active bursts can be selected by the user.

In each case, the I/Q-modulators 20 a and 20 b are connected to ahigh-frequency unit 22 a and/or 22 b, and a high-frequency signal can bepicked up at a bush 23 a and/or 23 b. For example, the output frequency,or several output frequencies initiated according to thesudden-frequency-change process from the high frequency unit 22 a and 22b, can be selected by the user.

Additionally, a signal display 24 is available, which can be connectedvia switch elements 25 a and/or 25 b in the exemplary embodiment to theoutput of the noise unit 15 a or the noise unit 15 b. Alternatively, itis also conceivable for the display device 24 to be connected directlyto the outputs from the base band units 2 a and 2 b. For instance, thesignal display 24 allows the configuration diagram to be displayed, sothat the user can check the method of operation of the connected signalpathway.

A Bit Error Rate Tester (BERT) 26 is also provided, and a signal fromthe device under test (DUT) can be supplied to the input bush 27 of theBERT 26, so that the bit error rate of the signal can be deducted at theoutput bush 28.

Other functional units may also be present and variant combinations ofthe functional units may be possible. These have not been explained herefor the sake of simplicity.

Using a combination unit 42, such as a directional coupler or a resistornetwork, the outputs 23 a and 23 b from the high-frequency units 22 aand 22 b may optionally be capable of further combination allowing thetwo signal pathways to be added on the high frequency side, if required,to form a combined signal. Accordingly, the two frequency-offset baseband signals may optionally each be modulated on two separatehigh-frequency pathways, so that only the two analogue high-frequencysignals are added. If the addition is carried out in the base band, theattainable signal dynamics are limited by the analogue-digitalconverter. This disadvantage is not encountered if the addition isimplemented in the analogue range. However, a greater degree ofcomplexity is required in this case. In this context, the two highfrequency pathways operate with the same carrier frequency. By contrastwith the solution of operating both high-frequency pathways withdifferent carrier frequencies and dispensing with the frequency offsetin the base band, this provides the advantage that only one frequencygenerator unit, for example, only one synthesiser, is needed to generatethe carrier frequency. This clearly leads to a reduction in complexity.

All of the functional units described above: 2 a, 2 b, 6, 8 a, 8 b, 8 c,9 a, 9 b, 9 c, 10 a, 10 b, 11 a, 11 b, 12 a, 12 b, 13 a, 13 b, 14 a, 14b, 15 a, 15 b, 16, 19 a, 19 b, 20 a, 20 b, 21, 22 a, 22 b, 24, 26, 40 a,40 b, 41 a, 41 b, 42 are connected to a control unit 28, for example, aCPU, via a control bus 29. Connections to the functional units areindicated by the symbol (*). The control unit 28 controls theconfiguration and function of the individual functional units requiredby the user. The current configuration of the functional units can bedisplayed on a display device 29, which can be disposed, together withthe operating elements 30, at the front of the signal generator 1. Forthis purpose, a graphic functional block is allocated to each functionalunit, and the connection of the functional units is displayed on thedisplay device 29 through corresponding connecting elements, whichconnect the functional blocks to one another. The connections betweenfunctional blocks and the function of the functional blocks are selectedeither by means of a rotary knob 31, appropriate operating buttons 32and/or via a mobile positioning element 33 (mouse).

While the present invention has been described in connection with anumber of embodiments and implementations, the present invention is notso limited but covers various obvious modifications and equivalentarrangements, which fall within the purview of the appended claims.

1. A signal generator comprising: at least one first base band unit anda second base band unit, configured for a digital base band signal, atleast one first frequency offset unit, coupled to the first base bandunit and configured for offsetting a frequency of an output signal fromthe first base band unit by a frequency offset, at least a secondfrequency offset unit, coupled to the second base band unit andconfigured for offsetting a frequency of an output signal from thesecond base band unit by a frequency offset, at least one first additionunit, configured for adding an output signal from the second base bandunit and an output signal from the first frequency offset unit, a firstI/Q-modulator coupled in series to the first addition unit, a secondaddition unit configured for adding the output signal from the firstbase band unit and the output signal from the second frequency offsetunit, and a second I/Q-modulator coupled in series to the secondaddition unit.
 2. A signal generator according to claim 1, wherein thebase band units are controlled in a synchronous manner by a commoncontrol unit.
 3. A signal generator according to claim 1, furthercomprising separate high frequency units connected in series to each ofthe I/Q-modulators, wherein the output signals from the high frequencyunits are combined in a combination unit.
 4. A signal generatoraccording to claim 1, further comprising: a fading unit configured forapplying fading and/or distortion to the base band signal, and connectedin series to each base band unit, and at least one further addition unitcoupled in series to the fading units by means of which output signalsfrom the fading units are added.
 5. A signal generator according toclaim 1, further comprising: a noise unit configured for applying noiseto the base band signal, and connected in series to each base band unit,and at least one further addition unit coupled in series to the noiseunits by means of which output signals from the noise units are added.6. A signal generator comprising: at least one first base band unit anda second base band unit, configured for a digital base band signal, atleast one first frequency offset unit, coupled to the first base bandunit and configured for offsetting a frequency of an output signal fromthe first base band unit by a frequency offset, at least a secondfrequency offset unit, coupled to the second base band unit andconfigured for offsetting a frequency of an output signal from thesecond base band unit by a frequency offset, at least one first additionunit, configured for adding an output signal from the second base bandunit and an output signal from the first frequency offset unit, anI/Q-modulator coupled in series to the first addition unit, a base bandgenerator, to which an external signal is supplied, configured forgenerating a digital base band signal from the external signal, and afurther frequency offset unit, coupled to the base band generator andconfigured for offsetting the frequency of the output signal from thebase band generator by a frequency offset, wherein the output signalfrom the further frequency offset unit is supplied to the first additionunit.